Grady/Fix Assessment Rendering

The problem was that we were using the .keys() method from where the assessments are in a dictionary. To avoid this kind of incorrect condensation, I separated the logic into a separate method (which can later be used to gate an author's view to not include AI if that is something we will pursue).
This logic is very similar in each of the test cases.  One way to make this more maintainable would be to put all the duplicate code in a helper method (maybe `assert_assessment_order(xblock)`), then have each of these test cases call that method.